Multifrequency transmission



MULTIFREQUENCY TRANSMISSION Filed Sept. 30 1931 INVENTQR gust HundATToNEY (am .nr .T0

Patented May 1, 1934 UNITED STATES MULTIFREQUENCY TRANSMISSION AugustHund, West Orange, N. J., assignor to Wired Radio, Inc., New York, N.Y., a corporation of Delaware Application September 30, 1931, Serial No.565,932

2 Claims.

My invention pertains in general to radio signalling and specificallyrelates to a system for simultaneously transmitting several programs.

One of the objects of my invention consists in providing amulti-frequency transmission system for simultaneously transmitting aplurality of Adifferently modulated discrete carrier frequencies.

Another object consists in producing a multifrequency transmissionsystem in which a plurality of discrete carrier frequencies aredeveloped from a common source of oscillations.

A further object comprises providing a system for multi-frequencytransmission in which relaxation oscillations are employed to develop aplurality of discrete carrier frequencies for individual modulation andtransmission.

I accomplish these and other desirable objects in a novel system formulti-frequency transmission in which a glow discharge tube relaxationcircuit serves to energize a plurality of high frequency circuits eachhaving individual modulation.

In the drawing accompanying and forming a part of this specification Ihave diagrammatical- 1y represented one embodiment of my invention asutilized for wired radio broadcasting over power lines.

In my co-pending application, Serial Number 561,837, filed September 9,1931, entitled Oscillation generator, there is disclosed, in moredetail, a system for producing relaxation oscillations by the agency ofa glow discharge tube; while in my co-pending application, Serial Number563,316, filed September 17, 1931, and entitled "High frequencygenerator and modulator, I have disclosed a system for producingrelaxation oscillations for the development of a plurality of commonlymodulated high frequencies.

Referring to the drawing in detail, there is provided a glow dischargetube 1 which comprises an envelope enclosing a pair of electrodes 2 and3. In the present embodiment of my invention this envelope is preferablyprovided with an attenuated atmosphere of helium. I have found thatsatisfactory results can be obtained by maintaining this atmosphere ofhelium at a pressure of substantially 12 mm. of mercury. It will beunderstood that other suitable gases can be used in lieu of helium andat other suitable pressures. The electrodes 2 and 3 are of a small areaand disposed in a manner such as to reduce interelectrode capacitance toa minimum. The electrodes 2 and 3 are connected with an external circuitincluding a resistance 4, a source of direct current 5, and aninductance 6, all connected in series.

Connections from the electrodes 2 and 3 are further extended to includea circuit having a variable condenser 10 connected in series with aplurality of oscillation circuits including the inductances 11, 12, and13, and the capacitances 14, 15, and 16, connected in parallel circuitsas shown. I have found in experiments that the capacitances 14, 15, and16, may sometimes be omitted when developing high frequencies inaccordance with my invention.

Inductances 11, 12, and 13 are electromagnetically coupled toinductances 17, 18, and 19, respectively. The inductance 17 is connectedbetween the control electrode and cathode of an amplifier tube 20. Theinductance 18 is connected between the control electrode and cathode ofan amplifier tube 21, and the inductance 19 is connected between thecontrol electrode and cathode of an amplifier tube 22. A capacitance 24is connected in parallel with the inductance 17 to form a resonantcircuit tuned to a definite high frequency suitable for carrier purposesin radio signaling. A capacitance 25 is connected in parallel with theinductance 18 to form a resonant circuit tuned to another high frequencywhich, in the present embodiment of my invention, is an integralmultiple of the fundamental frequency of the glow discharge system. Acapacitance 26 is connected in parallel with inductance 19 to formanother resonant circuit tuned to a still different frequency which hasan integral relation with respect to the fundamental frequency of therelaxation oscillations.

A condenser transmitter 28 is connected in shunt with the capacitance 24for effecting modulation, in accordance with sound waves incident uponthe condenser transmitter 28, of high frequency oscillations set up inthe circuit 17-24. Other condenser transmitters 29, and 30, aresimilarly provided with circuits 18-25 and 19--26, respectively.

'Ihe output or anode to cathode circuit of the amplifier tube 20includes an inductance 32 and source of anode voltage 33. The output oranode to cathode circuit of the amplier tube 21 includes an inductance34 and source of anode voltage 35, while the output or anode to cathodecircuit of amplifier tube 22 includes an inductance 36 and source ofanode voltage 37. The inductances 32, 34, and 36 are electromagneticallycoupled to inductances 39, 40, and 41, respectively.

These inductances 39, 40, and 41 are included in the input circuits toamplifiers 43, 44, and 45, respectively, which are connected to filters46, 47, and 48. Filter 46 is designed to pass only those frequencieswithin a range comprising the carrier and modulation side bandsappearing in the input circuit to amplifier tube 20. A similar relationexists between the filters 47 and 48 and their associated amplifier tubeinput circuits. The filters 46, 47, and 48 have their output circuitscapacitively coupled through condensers 49 to wire lines 50 connected toa source of commercial power 51. The power lines 50 and source ofcommercial power 51 are indicative of a power distribution networksupplying a multiplicity of consumers with commercial power.

In accordance with my invention, the source of current 5 applies apotential difference to the electrodes 2 and 3 which is of a magnitudesufcient to initiate a glow or ionization discharge in the glow tube l.The voltage necessary to bring about this glow discharge will be calledthe ignition voltage. If the resistance 4 is of a proper value, the glowdischarge which takes place across the electrodes 2 and 3 will produce apotential drop across the resistance 4, whereby the voltage across theelectrodes 2 and 3 will become reduced. As soon as the voltage acrossthe electrodes 2 and 3 becomes smaller than the lower critical voltage,the glow discharge will be quenched. 'Ihe foregoing functions will berepeated to produce continuous relaxation oscillations of a fundamentalfrequency designated as fo.

The inductance 6 forms a high .frequency choke which presents a highimpedance to high frequencies such as those designated as f1, f2, andf3, but presents a low impedance to lower frequencies such as the onedesignated as fo. It

will be apparent, then, that the inductance 6 subsantially prevents thepassage of high frequency currents through the relaxation oscillationcircuit without restricting the passage of the relaxation oscillationsat the fundamental frequency fo.

The relaxation oscillations produced by the glow discharge tube 1 andassociated circuit just described act through condenser 10 to produceimpulse energization of the circuits l1-14, 12-15, and l3-16. Thesecircuits have parameters of values such that this impulse energizationwill set up oscillatory currents of frequencies which are integralmultiples of the fundamental frequency fn' of the relaxationoscillations. The resonant circuit 17-24 is tuned to a desired highfrequency f1, a particular integral multiple of the fundamentalrelaxation frequency fo. This frequency f1 appears in the circuit 11-14and is selected by the circuit 17-24 for effecting the transfer ofoscillations at the desired frequency f1 to the amplifier tube 20 andcircuit that follows. These oscillations at the frequency f1 aremodulated under control of the condenser transmitter 28.

The resonant circuit 18-25 is tuned to another desired high frequency fzwhich is another integral multiple of the fundamental relaxationfrequency fo. The frequency f2 appears in the circuit 12-15 and isselected by the circuit 18-25 for effecting the transfer of oscillationsat the frequency f2, as modulated by the condenser transmitter 29, tothe amplifier tube 21 and following circuit. The resonant circuit 19-26is tuned to still another high frequency f3 which is an integralmultiple of the fundamental relaxation frequency fo. This frequency f3appears in the circuit 13--16 and is selected by the circuit 19-26 foreffecting the transfer of oscillations at the desired frequency f3,under control of the condenser transmitter 30, to the amplifier tube 22and following circuit.

The amplifiers 43, 44, and 45 increase the energy level of the modulatedhigh frequency currents of' the carrier frequencies fr, f2, and fa,respectively. The outputs of amplifiers 43, 44, and 45, are directedthrough the filters 46, 47, and 48 and are impressed upon the powerlines 50 for distribution to a multiplicity of consumers having theproper receiving apparatus for selecting any one of the desired carrierfrequencies each having separate program modulation. The fllters 46, 47,and 48 serve to restrict each program output to its particular frequencyrange.

It will now be apparent that my system for multi-frequency transmissionprovides for the production of relaxation oscillations by a glowdischarge tube for recurrently energizing a plurality of oscillationcircuits for producing sustained.

high frequency currents. These high frequency currents have frequenciesthat are integral multiples of the fundamental frequency of therelaxation oscillations and are selected at discrete high frequencies byselection circuits for individual modulation and transmission. AlthoughI have shown a preferred embodiment of my system for multi-frequencytranmission I do not desire to be limited thereto except insofar as maybe pointed out in the appended claims.

What I claim is new and original and desire to secure by Letters Patentof the United States is:

l. A system for multi-frequency transmission comprising, a plurality ofresonant circuits each comprising a capacitance and an inductance inparallel relation forming a tank circuit and each tuned to a differentfrequency, all of the frequencies being harmonically interrelated, arelaxation system comprising a resistance, an inductance, a source ofcurrent, a variable capacitance, and said plurality of tank circuitsconductively connected in series, a glow discharge device the electrodesof which are' conductively connected in series with said resistance,said inductance, and said source of current and in parallel with saidseries of tank circuits for recurrently energizing said relaxationcircuit, amplifiers, individually coupled to each of said tank circuits,individual modulation circuits coupled between said amplifiers and saidtank circuits and the output circuits of all of said amplifiers beingconnected to a common transmission line.

2. A system for multi-frequency transmission comprising, a plurality ofresonant circuits each consisting of a condenser and an inductanceconnected in parallel relation to form a tank circuit and each tuned toa definite different frequency, the frequencies being harmonicallyinterrelated, a relaxation oscillation circuit comprising a resistance,an inductance, a source of current, a variable capacitance, and saidplurality of tank circuits all conductively connected in series, a glowdischarge device the electrodes of which are connected in seriesrelation with said resistance, said inductance and said source ofcurrent and in parallel relation with said series of tank circuits forrecurrently energizing said relaxation oscillation circuit, a commontransmission line and separate circuits, each including a modulationcircuit, an amplifier and a filter connecting said tank circuitsindividually through condensers with said common transmission line.

AUGUST HUND.

